High-strength, high-toughness (iron-carbon-nickel-molybdenum) steel weld metal

ABSTRACT

An alloy is described which is suitable for use as a weld-filler material and which is characterized by having controlled strength and toughness. The composition includes about 4.5 percent nickel, 2 percent molybdenum, up to 0.35 percent carbon, low impurity and interstitial content, and the balance iron. The strength is controlled in accordance with the relationship:

Unite n 1151 women 1ensehkel [45] Alan. 11E, Lil "ill [54] HIGH-STRENGTH, HHGH-TOHJGHNESS 2,150,785 3/1939 Roolte ..75/123 K x (IRUN QAMMUN N]HCMEL. 2,707,680 5/1955 Succop ..75/1231 MOLYEDENIUM) STEEL WELD METAL [72] Inventor: ,llulius lilleuschltel, Irwin, Pa.

FOREIGN PATENTS OR APPLICATIONS 524,566 8/1940 Great Britain ..75/123 1( [73] Assignee: Westinghouse Electric Corporation, Pitt- Sburgh, Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Joseph E. Legru [22] F11ed: Apr- 7, 1970 A!t0rney-F. Shapoe [21] App1.No.: 26,230 [57] ABSTRAQT 52 us. at ..75/123 ,1, 75/123 K alloy descnbed whch sumble use as a (322C 37/00 material and which is characterized by having controlled K 123 J strength and toughness. The composition includes about 4.5 percent nickel, 2 percent molybdenum, up to 0.35 percent carbon, 10w impurity and interstitial content, and the balance [51] lint. Cl [58] Field of Search [56] References Cited iron. The strength is controlled in accordance with the relationship: UNITED STATES PATENTS 0.2 percent yield strength=52 1(.s.1. 268.4 I(.s.1. C ,742 4/1918 Churchward ..75/123 K where C is the carbon content ofa weldmem made from the 1,261,743 4/1918 Churchward.... ..75/123 K alloy in weight percent. 2,026,418 12/1935 Crowe ...75/123 K X 2,060,765 1 H1936 Welch ..75/123 K X 5 Claims, 2 Drawing Figures 2200 A 5 5 r( I 1.1. E 0 g E 2 4a! LLJ 5120 5 3 Y5 q) 2 L, H m E 80 a a k E o L) 40 o 0 l l J l I I l I O 0 .10 2O .30 .40

Weld Carbon Content (W171) PATENTED JAN] 81972 SHEET 2 0F 2 5. 3: 22 GO ON (w mp/(5.10113 u31o Mum 5% C) CD a 9: (M 0001) 1 08+ 1 41 15 m m "AZ'O H H EC VS NU IIIE H S U U U 0 2; a: we; 230v 23. 8 2 Q a; ea; 58d 28s as: 325 amass fifilfifi M wwwoe flood 630v See moodv 590 a; Edv a: n86 @830 $86 was a So mas Q so so m8 ov S o 2. H 2 d 5 a 3e 0 .03 no a8 $8 6 8 e E2 A W830 286 0 @206 83v 830 2a 5 0V m: we: 8: e8: $8 6 5 0 e W 0% 386v 38 0 82v 83 82v 3 0 a: a; a? Q85 5; $86 88 3 8 e M B2 A 38 0 $2; 830v Sod m ev 8d 2 m adv $0 2: 25 o $8 0 88 a a 0 886 age 56 we: 22v 2; 21 26 as 230 2; 886 885V 5 o W N886 88d 530v 80 0 82v 8: m; :Zv a: 330 52v 386 886v 2:

$8 0 $8 6 :sev 830 82v 8d of m was 2.; 086 as: we: 5 Q W E: W m8; 885 S30 82 82v 89 2 N. adv as S: 52v $8 :8 5 0 e 88 e 28 Q So 2o 0 8c ov 5 o 8 N E d 2 a OS 0 c8 6 8 88 o 8 0 w 32 u 286 88d 52v 8: 32V 5 0 we m adv e3 es 0 a8 a :8 e 28 o 8 o 8. 0 A i 0 E. 2 0 i :0 a w a :2 0 29s 52 55 ce :3 mme m 5 z 23 c a 2 5 5 52 3 m cccmwoboo $093313 M2500 2.69000 come Qza 3:02 ESQE mo mzorimomzoo a 0 5 0 5 4 mm 4 M l-lllGl-l-STRlENGTll-ll, lillllGlll-TOUGHNESS (IRON-CARBON- NllClltEL-MOLYBDENUM) STEEL WELD METAL BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a composition of matter which is suitable for use in producing high-toughness characteristics in a weldment of either lowor high-strength. The composition of matter is more particularly an alloy and the alloy having a given compositional limit may be manufactured in any desirable form, for example, that of a welding rod or wire.

There has been a constant demand for further improvement in the properties of ferrous-base materials which have been 15 utilized as weld-filler materials both from the standpoint of strength and of toughness. This continued desire to improve and control these properties has led to the investigation of the efiects of alloying elements on the properties desired to be controlled.

More significantly, considerable research has been conducted in which the function of the various alloying components, which are normally found in steel materials, was varied in order to determine the effect on the as deposited" and the stress-relief-annealed properties of strength and 25 toughness of weldments produced therefrom. Such a study indicated that the elements manganese, silicon copper, chromium and tungsten, while being found in various quantities in materials subject to weldments or which actually form a part of the weld-filler material itself produce no significant contribution to the strength characteristics of the weldmentfi Furthermore, since additions of these elements tend to decrease weld-toughness their presence is not particularly necessary nor desirable. However, it must be pointed out that the weld materials may contain certain amounts of manganese and silicon in order to fabricate the composition into a usable product in the form, for example, of a welding rod. in addition, the manganese and silicon may also function to produce sounder welds in the materials which are undergoing a welding operation thereby contributing to the overall desirability of their presence within the composition within limited amounts. Essentially however, it was found that so long as the manganese was kept below 0.10 percent and the silicon below about 0.05 percent, sufficient ductility and workability was achieved within the alloy composition to enable the same to be readily hot' and cold-worked and produce sound welds without unduly detracting from the strength or toughness characteristics exhibited by this metal.

it has also been found that additions of vanadium and cobalt 5Q definitely decrease the strength characteristics of steel-weld ing materials and accordingly should be avoided. Moreover, since such elements as aluminum, titanium and zirconiumv were found to be detrimental to weld metal-toughness, the useful choices for alloying steel weld materials were limited to 55 the elements carbon, nickel and molybdenum. Both nickel and molybdenum are readily controllable both in the steelmelting practice and during transfer across the welding are from filler metal to weld deposit. The only necessary variation in the weld composition is that of the carbon content and such carbon content has been found to significantly influence the weld properties. Thus by the simple expedient of making a check analysis for carbon on each lot of welding wire, the probable weld deposit strength and toughness classifications can be made and as a result thereof the weld quality can be accurately controlled.

SUMMARY OF THE INVENTION The present invention relates to a material suitable for use us a weld-filler material and consists of an alloy having a composition of between about 4.25 and about 4.75 percent by weight of nickel, from about L to about 2.25 percent by weight of molybdenum, up to about 0.35 percent by weight carbon and the balance essentially iron with incidental impuri- 75 ties. These incidental impurities include residual amounts of manganese, silicon, copper, chromium, vanadium, titanium, and cobalt, as well as low amounts of interstitial elements such as not more than about 0.004 percent phosphorus and sulfur, about 0.003 percent nitrogen and about 0.002 percent oxygen. The alloy in its welded condition is controlled so as to provide a 0.2 percent yield strength within the range between about 52 k.s.i. and about 200 k.s.i. in accordance with the relationship:

0.2 percent yield strength 52 k.p.s.i. 268.4 k.p.s.i. C where C is the carbon content in weight percent of the weld deposit.

DESCRIPTION OF THE DRAWING FIG. 1 is a plot of the 0.2 percent yield strength and Charpy V-notch energy values versus the carbon content of the weld metal in the as deposited condition; and

FIG. 2 is a plot of the 0.2 percent yield strength and the Charpy V-notch energy versus the carbon content of the weldment after annealing for 8 hours at a temperature of 1,05 F. following welding.

DESCRIPTION OF THE PREFERRED EMBODIMENT The alloy of the present invention is suitable for use as a weld-filler material and consists essentially of by weight from about 4.25 to about 4.75 percent nickel, from about 1.75 to about 2.25 percent molybdenum, up to about 0.35 percent carbon and the balance essentially iron. The alloy is characterized by having a 0.2 percent yield strength within the range between about 52 k.s.i. and about 200 k.s.i. in accordance with the relationship:

0.2 percent yield strength 52 k.p.s.i. 268.4 k.p.s.i. where C is the carbon content in weight percent of the weld deposit. In this respect it should also be noted that it is necessary, and in fact highly critical, to maintain the interstitial content at as low a level as is practical commensurate with good metallurgical practice. In this respect, it is desired that the phosphorous and sulfur contents do not exceed about 0.04 percent, and the nitrogen content being less than about 0.003 percent and the oxygen content being less than about 0.002 percent. Typical levels of such other components include 0.05

max. silicon, 0.10 max. manganese, 0.05 max. copper, 0.3,

max. chromium, 0.02 max. vanadium, 0.003 max. titanium, and 0.01 max. cobalt.

in order to more clearly demonstrate the alloy of the present invention, reference may be had to table I which lists a series of compositions of filler metals and weld deposits which were made and tested in accordance with the present invention.

In conducting these tests five experimental heats were originally requested, the same to contain about 4.5 percent nominal nickel, 2.0 percent nominal molybdenum with a varying carbon content of 0.05, 0.10, 0.15, 0.20 and 0.25 weight percent carbon. All other elements were to be as near zero as 5 possible, with the remainder of the alloy being iron. Actual chemical analysis indicates from table I that the nickel content ranged between about 4.25 and about 4.73 percent while the molybdenum content ranged between 2.08 and about 2.12 percent in the actual welding wires as the same were melted. However, insofar as the components of the weldment composition were determined, the nickel content ranged from 4.13 to about 4.67 percent while the molybdenum content varied between about 1.96 and about 2.23 percent. Thus it can be seen from the foregoing that a very good control can be maintained within the metal composition both in its steelmelting analysis as well as in the afterwelding weld metal analysis, the latter being in part influenced by the composition of the base metal being welded. The data contained in table I for the weld metal compared with the wire analysis indicates that excellent alloying component transference has occurred through the welding arc thereby assuring that the compositional quality of the weld can be accurately controlled.

The five experimental compositions were formed into welding wire and were converted into welds in an environment of pure argon using a tungsten arc to melt the wire to form the welds. These welds were utilized to join plates having the following composition:

Carbon 0.17 Nickel 3.53 Manganese 0.35 Chromium 1.64 Phosphorus 0.007 Molybdenum 0.29 Sulfur 0.009 Vanadium 0.11 Silicon 0.23 Nitrogen 0.0028 Copper 0.1 1 Oxygen 0.0018

The composition of each deposited weld as shown in table I is close to that of the corresponding wire, the primary difference being there was an increase in the copper and chromium content. This resulted from the face that the plate contains a substantial amount of these two elements. With these relatively minor exceptions, the weld metals were essentially the same as the final composition of the corresponding weld wire used.

After welding, both tensile and impact specimens were made from these welds in both the as-deposited condition as well as after stress-relief-annealing of the weldment for about 8 hours at a temperature of 1,050 F.

Reference is directed to table 11 which lists the tensile and impact properties of the weldments employed in the asdeposited" condition having the identification as set forth hereinbefore in table 1.

TABLE II.-WELI) METAL PROPERTIES (AS-DEPOSITED CONDITION) Weld No.

Loading cycle No.1 No.1 No.1 No.2 N0. 2 No.1 No. 1

+80 F. tensile properties:

Stresses (p.s.i.):

Prop. 11m 126, 000 142, 200 174, 000 108, 750 104, 500 200,000 190, 000 0.2% yield 131,100 160,400 100,800 202,000 202, 500 207,000 200,000 0 5% yield 130,800 173, 400 1117, 000 197, 000 108, 000 206, 500 200,250 Ultimate 136, 400 178, 500 1 200, 000 202,000 202, 500 210, 500 207, 000 True fracture 321, 500 337, 800 Unbroken 331 800 360, 850 334, 300 313. 700 Ductility (percent):

Elong, 1. .18 El0ng.,uni1..... 8.25 7.56 7. 4 8.0 Eloug., total 25. 05 21. 35 14. 0 12, 0 Area red 7 0 54. 4 -14. 8 Charpy V-notch energy,

values (lt.-1h.):

171.0 24 & 170.0 82. 00

I Loading stopped at 200,000 p.s.i. and specimen transferred to larger testing machine designated as No. 2. 2 True '1otal=1fi.1%,i.e., 15ul+0.7%.

From the data set forth in Table 11 it becomes apparent that the alloy of the present invention has excellent strength together with excellent toughness even at temperatures below room temperature. 1n this respect it is noted that increasing the carbon content in the range indicated in Table 1 is effective for increasing the 0.2 percent yield strength from about 131 k.s.i. up to a value in excess of 200 k.s.i. This strength is attained with excellent elongation and reduction of area. Concomitantly, it may be noted that with the higher carbon contents the toughness is reduced; however, it is noted that even at temperatures as low as 200 F. the metal still has in excess a 20 ft./1b. of energy absorbed, a condition which is highly desirable considering the demanding service condition arising at 200 F. temperature.

In order to more clearly demonstrate the outstanding strength and toughness properties exhibited by the alloy of the present invention, reference is directed to FIG. 1 which plots the carbon content of the weldment versus the yield strength and the Charpy V-notch energy absorbed both at room temperature and at a temperature of 60 F. In FIG. 1 the curve represents the 0.2 percent yield strength while the curve 12 illustrates the Charpy V-notch energy curve when measured at a temperature of 80 F., and curve 14 is the same Charpy V- notch value when measured at a temperature of -60 F. From curve 10 it can be seen that the carbon content of the weld- .ment has a well-defined relationship to the exhibited yield strength. Curve 10 indicates that the yield strength as measured will vary in the following manner:

0.2 percent yield strength 52 k.p.s.i. 268.4 k.p.s.i. /C where C is the carbon content of the weldment in weight percent. This appears to be the equation which most closely prediets the yield strength based on the carbon content of the weld from the data contained in Table 11 and curve 10 in particular.

Thus, FIG. 1 indicates that an 80,000 p.s.i. yield-strength weld metal can be obtained using about 0.02 percent carbon in addition to about 4.5 percent nickel and 2.0 percent molybdenum. This provides a Charpy V-notch energy value of about 240 ft./lb. across the temperature range from 50 F. to +80 F. which constitutes an exceptionally high toughness level. Moreover, a 130,000 p.s.i. minimum yield-strength weld metal can be deposited by providing a minimum value of about 0.1 weight percent carbon. Such deposit results in a maximum impact energy value of 196 ft./lb. at 60 F. Similarly, a 150,000 p.s.i. minimum yield-strength weld deposit can be secured by the addition of a minimum of about 0.14. weight percent secured by the addition of a minimum of about 0.14 weight percent carbon, such carbon level resulting in an impact energy value of up to 145 ft./lb. at 60 F. Achievement ofa level of about 20 ft./lb. at this last temperature is commonly considered to be in high strength weldments. In addition thereto, a

200,000 p.s.i. yield-strength weld deposit can be obtained with this alloy when a minimum of about 0.3 weight percent carbon is provided in the deposit. A weld deposit of such an alloy composition has an impact energy absorption of up to 38 ft./1b. at F. Since in some cases, such as when residual welding stresses must be reduced to minimize or prevent stress corrosion cracking in a sea-water environment, it is desirable to thermally stress-relief-anneal a welded structure prior to use. This requires that the weld metal be able to withstand the imposed thermal cycling without excessive deterioration of its mechanical properties. An important criteria is not whether or not there is an actual loss or gain in the impact values as a consequence of the thermal treatment but rather, are the resulting values adequate to meet the intended service requirements. Ordinarily, a 50 ft./lb. value at F. and a 20 ft./lb. value at -60 F. is considered adequate for very demanding service conditions.

Reference is now directed to Table 3 and P16. 2, which i1- lustrates the relationship between the carbon content and the yield strength as well as the Charpy V-notch energy absorption of the same materials after stress-relief-annealing for 8 hours at a temperature of 1,050 F. In IFIG. 2 the curve 20 is a plot of the 0.2 percent yield strength versus the carbon content whereas the curve 22 is that of the Charpy V-notch energy versus the carbon content when measured at 80 F. and curve 24 is the same plot when measured at a temperature at 60 F. By comparing both curve 10 and curve 20 of FIGS. 1 and 2, respectively, it will be immediately apparent that the yield strength is directly related to the square root of the car' bon content, the only difference being in the value of the zero carbon intercept between the material in the as-deposited condition and the material in the stress-re1ief-annea1 condition. Thus, since the chemical composition can be controlled both in melting as well as in transference through the welding are it becomes clear that a close control can be exercised over the quality of the welds made from materials produced in accordance with the teaching of the present invention.

Reference to FIG. 2 will indicate that such conditions are easily met by the composition of the present invention. Thus these data demonstrate that any desirable 0.2 percent yield strength within the 80 and 200,000 p.s.i. range can be ob ;tained after a 1,050 F. soak for 8 hours with a slow heating TABLE llL WELl) 1\'1 ETAL PROPERTIES (ANNEALEI) 8 HRS. AT 1050 F.)

Weld No.

Loading cycle a No.1 No. 1 No.1 No. 2 No. 1 No.2 No.1 No.1

+80 1'. tensile properties:

Stresses (p.s.i.):

Prop. limit d 12-1, 400 153, 400 162, 000 180, 300 167, 800 117, .100 105, 000 215, 450

0.2% yield 133, 200 170, 400 106, 500 185, 800 181, 200 100, 250 201 500 117,050 0.5 yinliL 134, 800 A h 155, 800 180, 200 101, 050 100, 750 208,150 Ultimate 140, 800 200, 000 185, 800 200, 200 106, .250 202, 500 217, 050 True ltactnl'tx 310, 500 216, 500 Unbroken 280, 000 Unbroken 277,150 242,150 .203, 050 [)nctility (percent): Elongation:

Uniform 5.85 A v 0.43 0.2 0.1 .1 '1 .20. 05 0. 35 0. .38 13. 1 1.15 3 0. 0 11.0 T2. .20 10.10 Unln'okvn 02. 3 Unbroken 44. 5 27. 0 2 Charpy \'-noteh energy t11L1l'S ft. 11).) at

tvrnpt-ratln'v listed:

+200 F. 110.0 05.0 13.5 10.0 +00 F" 105.5 65.0 12.5 10.0 +32 F... 114. 0 50. 0 11.0 T. 5 0 F a 107. 0 05. 5 10. 0 T. t)

1375 It is repent tcst011375. Loading stopped at 200,000 p.s.i. and specimen trnnsfvrlwi in lznur-r testing machine designated as No. 2.

True total-13.38%, i.v., 131-0280}. "lrun total 10.45"/}, ism, 0.3 1.15%.

From the foregoing, it is clear that there has been provided a welding system wherein the alloy makeup and the balance itself to provide a built-in quality control with respect to properties, particularly above the 130 k.s.i. yield-strength level. Since the molybdenum and nickel contents are readily controllable both in the steel-melting practice and during transfer across the welding are from the tiller metal to the weld deposit, only variations in the carbon content significantly influence the final weld properties. Thus the alloy finds wide use in joining various ferrous base materials with only minor dilution which does not significantly affect the mechanical properties. Above about 0.10 percent carbon the strength response to carbon content variations is a minimum on a unit weight percent basis. By the simple expedient of making a check analysis percent basis carbo n on each lot of welding wire, the probable weld deposit strength and toughness classification can be made thereby affording an excellent and accurately controlled prediction of weld quality.

In addition, the system is equally applicable for use in both the as-deposited or in the stress-relief-annealed conditions. The alloy system thus enables the attainment of controlled high-strength properties together with concomitant toughness properties in order to obtain an outstanding composition suitable for use as a weld-filler material.

lclaim:

1. An alloy suitable for use as a weld metal consisting essentially of, by weight, from about 4.25 to about 4.75 percent nickel, from about 1.75 to about 2.25 percent molybdenum, up to about 0.35 percent carbon and the balance essentially iron, said alloy in the as-welded condition having a 0.2 percent yield strength within the range between about 52 k.s.i. and about 200 k.s.i. in accordance with the relationship:

3 v y e i K-.R-.-L EZQAK-P- VC where C is the carbon content, in weight percent, of the weld deposit, said alloy being further characterized by low interstiwtial content and not exceeding about 0.004 percent phosphorus, about 0.004 percent sulfur, about 0.003 percent nitrogen and about 0.002 percent oxygen.

2. The alloy of claim 1 in which the nickel content is nominally about 4.5 percent and the molybdenum content is nominally about 2 percent.

3. The alloy of claim 1 in which the carbon content is limited to a range between about 0.10 percent and about 0.30 percent, said alloy having a minimum 0.2 percent yield strength of about k.s.i. and Charpy V-notch impact energy value of about 40 ft./lb. at a temperature of 60 F. in the as-deposited condition.

4. A weld rod suitable for producing high strength and high toughness in both the as-deposited and the stress-relieftoughness condition and formed of the alloy having the composition'of claim 1.

5. A weld-filler material suitable for producing high strength and high toughness in a weldment, said material having a composition consisting essentially of, by weight, from about 4.25 to about 4.75 percent nickel, from about 1.75 to about 2.25 percent molybdenum, from about 0.10 to about 0.30 percent carbon and the balance essentially iron with not more than the following listed impurities:

0.004 phosphorus 0.004 sulfur 0.003 nitrogen 0.002 oxygen 

2. The alloy of claim 1 in which the nickel content is nominally about 4.5 percent and the molybdenum content is nominally about 2 percent.
 3. The alloy of claim 1 in which the carbon content is limited to a range between about 0.10 percent and about 0.30 percent, said alloy having a minimum 0.2 percent yield strength of about 130 k.s.i. and Charpy V-notch impact energy value of about 40 ft./lb. at a temperature of 60* F. in the as-deposited condition.
 4. A weld rod suitable for producing high strength and high toughness in both the as-deposited and the stress-relief-toughness condition and formed of the alloy having the composition of claim
 1. 5. A weld-filler material suitable for producing high strength and high toughness in a weldment, said material having a composition consisting essentially of, by weight, from about 4.25 to about 4.75 percent nickel, from about 1.75 to about 2.25 percent molybdenum, from about 0.10 to about 0.30 percent carbon and the balance essentially iron with not more than the following listed impurities: 0.004 % phosphorus 0.004 % sulfur 0.003 % nitrogen 0.002 % oxygen 